Particulate refractory inorganic oxide solids, e.g., alumina, have been employed for many years as catalyst supports, or carriers, in natural or synthetic form. For example, synthesis gas, or syn gas (hydrogen and carbon monoxide), is produced from low molecular weight hydrocarbons, primarily methane, reacted in the presence of steam (steam reforming process) or oxygen (partial oxidation process), or both steam and oxygen, at high temperature within a fluidized bed of catalyst, e.g., nickel on an alpha alumina support. Frequently, a second catalytically active solid is present in minor amount to promote the steam reforming reaction. Suitably, particulate refractory inorganic oxide solids, notably alpha alumina solids, are admixed with the catalyst, or catalysts, of the fluidized bed as heat transfer solids to control the temperature of reaction. Processes utilizing the admixtures of catalysts and heat transfer solids in reacting low molecular weight hydrocarbons in the presence of both steam and oxygen, it has been found, have provided overall high thermal efficiencies in the production of syn gas.
Certain particulate refractory inorganic oxide solids as heat transfer materials are more resistant than others to melting and agglomeration at the severe high temperature oxidizing and reducing conditions encountered in fluidized bed syn gas generation processes. These particulate refractory inorganic oxides permit substantially isothermal reactor conditions in conducting such reactions, at least so long as they resist melting and agglomeration which leads to reduced fluidization quality, gas bubbles of increased size, and inferior mass transfer. Moreover, the mechanical strength of some particulate solids is greater than others, and in any process the particles must be sufficient to withstand the stress and strain of process operations.
Sintering and agglomeration of the fluidized bed solids have been found particularly important pathways for fluidized bed degradation, and loss of catalyst activity in fluidized bed operations. Hot spots, particularly as occurs in the zones of oxygen injection, produces sintering and agglomeration of the particles. The temperatures in these zones far exceed the normally high temperature of reaction outside these zones, often by several hundred Fahrenheit degrees. Surface melting of the particles, for any reason whatever, creates a tendency of the particles to fuse, or stick together to form agglomerates; and agglomeration of the particulate sol ids promotes defluidization of the bed. Particulate heat transfer solids must also be chemically compatible with the catalyst of the fluidized bed for contamination and poisoning of the catalyst cannot be tolerated. Albeit there are a few which stand out as exceptional in a relative sense, no particulate refractory oxide solid is now known which possesses the combination of properties which would render it a heat transfer solid capable of completely withstanding sintering, agglomeration and attrition to the desired degree at the extreme conditions encountered in commercial fluidized bed syn gas operations, particularly commercial fluidized bed syn gas operations at extreme hydrothermal conditions. Thus, there exists an acute need for further improving and maintaining the fluidization characteristics of the bed, or beds, employed in fluidized bed synthesis gas manufacturing processes.